Here are the options that Thorn provides for your additional training over the next month:

“Deception is a tool. Master it.”- +1 to all deception checks

“Discover what is real, and what is illusion.”- +1 saves vs illusions

“Fear nothing, except or dread mistress.”- +1 saves vs fear

“Focus strengthens your will.”- +1 saves vs charm/compulsion effects

“Be calm in the face of adversity”- +1 concentration checks

“Let us perfect your favorite spell.”- Pick one spell that you can cast now. If it is a damaging spell, it does 1d4 additional damage every time you cast it. If it is a save vs an effect, that DC is +1. If a spell has both, you pick one or the other bonus and that one type of bonus is what you always get.